1. Field of the Invention
The invention relates to a method for manufacturing a prosthesis for replacing at least one tooth, the prosthesis being arranged for insertion in a patient's jawbone, the prosthesis comprising an implant and an abutment in accordance with the preamble of claim 1. Also, the invention relates to a method for manufacturing a drill guide for use with the manufacturing of the prosthesis. Moreover, the present invention relates to a prosthesis comprising an implant and an abutment. Furthermore, the present invention relates to a drill guide for use in a patient's jaw bone without the need for a flapping operation. Also, the present invention relates to an impression tray for taking an impression of a denture of a patient. The present invention also relates to a computer system and a computer program product for manufacturing a prosthesis for replacing at least one tooth.
2. Description of the Related Art
Dental restorative systems seek to provide cosmetic and functional replacements for missing teeth. A dental restorative system that replaces a single tooth typically includes three components. These are the dental implant fixture, the abutment, and the crown. The dental implant fixture anchors the restorative system to the jawbone. The crown replicates the contour and appearance of the visible portion of the restorative system to match that of the natural dentition. Finally, the abutment connects the crown to the dental implant fixture. The abutment also holds the crown in proper alignment relative to the implant fixture, and absorbs the stress of chewing. A customized abutment should also match the size, shape and contour of the original tooth in order to provide the best possible appearance. In the prior art, the crown and the abutment consist of two separate parts. The abutment is screwed onto the implant and then the crown is cemented on the abutment, covering the screw of the abutment.
Standard methods for preparing dental restorative systems require considerable time, labor, and expense. Methods typically require that the patient make between six and ten visits to the dentist's office to complete installation of the restorative system. An oral surgeon or periodontist is required to surgically implant the dental implant fixture into the patient's jawbone. A general dentist or prosthodontist typically performs the measurement and fitting of the abutment and crown, and a technician typically sculpts the abutment and crown.
It is known in the art to secure dental prostheses using dental implants secured in the upper or lower jawbone. It is also known in the art to mount a framework or superstructure to a number of implants, the superstructure being used to evenly support a set of false teeth or denture prostheses. Accurate placement within the jawbone of the implants is a difficult task. In International Patent Application WO 94/26200, there is described an adjustable guiding device for positioning dental implants in which it is possible for the dental surgeon to adjust a drill axis for each implant before proceeding to use the guiding device or drill template to guide the surgeon's drill for the purposes of preparing the drill hole for the implant. The guiding device disclosed in WO 94/26200 helps the dental surgeon to decide on the drill axis after viewing radiographic images of the radio-opaque tubular drill guide superposed on the bone structure.
In the prior art, the oral surgeon typically has difficulty deciding on a drill axis for the implants since the ideal position for the implants should be decided with knowledge of the jawbone structure into which the implant is to be inserted, knowledge of the position within the jawbone structure of the nerve tissue, the gum surface and the required position and dimensions of the false teeth or dentures to be supported by the dental implant. In the conventional manner of selecting the implant axis, the dentist or dental surgeon simply makes a best guess in light of his knowledge of the patient. Of course, this leads, in certain cases, to imperfections in the dental prosthesis (see also: Massey, B. C.; Alder, M. E.: Analyzing Implant Placement in the Posterior Maxilla, J Dent Res, Abstr 3554, 2002).
The imperfections may relate to a lack of ideal support, an unfavorable angulation of an implant causing a weakness in the implant which may cause failure over time, or a visually perceptible defect in the appearance of the prosthesis.
In the conventional method for the construction of the superstructure, a physical model of the patient's gums and dental implant heads is prepared on which the superstructure is built manually using molding and other techniques known in the art. The craftsman or technician skilled at manufacturing such dental superstructures takes into consideration the size and shape of the desired dentures to be placed over the superstructure when crafting the same.
The procedure for manufacturing dental implant superstructures as known from the art is time-consuming and sometimes results in imperfect structures or defects in the visual appearance of the dentures to be placed over the superstructure.
U.S. Pat. No. 6,382,975 describes a method for manufacturing a dental implant drill guide and a dental implant superstructure in the form of a fixed dental prosthesis or an overdenture. The method comprises the manufacture of a scannographic scanning guide with reference spheres in specific positions. Disadvantageously, such a scannographic guide requires the manufacture of a jawbone model based on a physical model of the jaw.
U.S. Pat. No. 5,989,029 describes a method for the provision of a customized dental abutment which replicates a tooth being replaced. The dimensions of the abutment are determined by a computer algorithm that is capable of modifying standard tooth type models according to a series of measurements taken of the site of desired tooth replacement, i.e., the location for the replacement tooth. The method describes taking a series of measurements of the site of the desired tooth replacement, determining the type of tooth being replaced, and preparing or selecting a customized dental abutment based on the measurements and determination. The preparation or selection is made by modifying standard measurements for the type of tooth being replaced in conformity with the measurements taken of the site of desired tooth replacement. Disadvantageously, only discontinuous lines may be extracted from the model to modify a generic abutment parametrically and only so by selecting standard measurements that are entered.
WO 03/045268 describes a ceramic implant consisting of zirconia-based material and at least sections of the external surface of at least the anchor part are pre-treated using a subtractive method or are provided with a coating which supports ossification. Disadvantageously, the implant is treated after the material has reached its final density, which basically renders the material bio-chemically inert with respect to dental treatments.
In PCT/BE95/00033 a method is set fourth for making a perfected medical model on the basis of digital image information of a part of the body. The digital image information of a part of the body is converted, by means of what is called the rapid prototyping technique and thus with a processing unit and a rapid prototyping machine, into a basic model of which at least a part perfectly shows the positive or negative form of at least a portion of the part of the body. At least an artificial functional element with a useful function is added to the basic model as a function of the digital information and possibly as a function of additional external information. However, the models produced up to now, including three-dimensional images, do not take advantage of all the information contained in the image information. They form a perfect copy of the part of the body, but they do not contain any additional functional elements. Such models which are exact copies of real structures are for example produced from medical images with the technique disclosed in the article “Integration of 3-D medical imaging and rapid prototyping to create stereo lithographic models” from T. M. BARKER et al., published in “Australasian Physical & Engineering Sciences in Medicine”, vol. 16, no. 2, June 1993, pages 79-85. Scanner data are transformed to a suitable format in a computer and the images are processed as a volume of so-called voxels (a volume pixel). The object is segmented prior to the meshing of the object surface and the creation of a stereo lithographic model. The obtained model cannot be used for registration, i.e., correlate to a position on the patient. Functional elements, such as an opening indicating the place and direction for drilling, can be added manually, but not as a function of the image information.
The information or data set from tomographic scanning, consisting of voxels and contours, can be converted into a set of contours per layer height. By using the grey scale value information in the image it is possible to increase resolution by working with sub-voxel resolution, as described by B. Swaelens and others in “Medical Applications of Rapid Prototyping Techniques”, p. 107-120 of “Proceedings of the Fourth International Conference on Rapid Prototyping, Dayton, Ohio, Jun. 14-17, 1993”. However, disadvantageously, this higher resolution is still insufficient to make a drilling guide fit perfectly on the mucosal surface or remaining dentition, even when the contours per layer are calculated to the layer height which is suitable for the rapid prototyping technique which is usually significantly lower than the scan distance. Disadvantageously, to obtain a sufficient higher resolution in the prior art would require higher X-ray doses and/or longer exposure times for a patient. Such additional exposure to high energy radiation may pose an increased risk for a patient health and is therefore clearly unwanted.
Moreover, PCT/BE95/00033 discloses that if an external element is added to the CT scan image this external element must be represented as voxels or contours as well, by means of cross section and shading algorithms. After an interactive processing of the image information (e.g., rotations, translations, etc.), it is necessary to return to the original CAD data for obtaining a higher accuracy of the inner surface of the drill guide. Clearly, such human-assisted processing must be elaborate and will require a large effort in processing time and costs.